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          <h1 class="post-title" itemprop="name headline">Java-ThreadLocal使用</h1>
        

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        <p>###Java ThreadLocal使用</p>
<p><strong>ThreadLocal类允许我们创建只能被同一个线程读写的变量。因此，如果一段代码含有一个ThreadLocal变量的引用，即使两个线程同时执行这段代码，它们也无法访问到对方的ThreadLocal变量。</strong><br><a id="more"></a></p>
<p>1.如何创建ThreadLocal变量<br>以下代码展示了创建ThreadLocal变量的三种方式：<br>方式一：直接创建对象<br><code>private ThreadLocal myThreadLocal = new ThreadLocal();</code><br>方式二：创建泛型对象<br><code>private ThreadLocal myThreadLocal = new ThreadLocal&lt;String&gt;();</code><br>方式三：创建泛型对象及初始化值<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">private ThreadLocal myThreadLocal = new ThreadLocal&lt;String&gt;() &#123;</span><br><span class="line">    @Override</span><br><span class="line">    protected String initialValue() &#123;</span><br><span class="line">        return &quot;This is the initial value&quot;;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure></p>
<p>通过代码实例化了一个ThreadLocal对象。我们只需要实例化对象一次，并且也不需要知道它是被哪个线程实例化。虽然所有的线程都能访问到这个ThreadLocal实例，但是每个线程却只能访问到自己通过调用ThreadLocal的set()方法设置的值。即使是两个不同的线程在同一个ThreadLocal对象上设置了不同的值，他们仍然无法访问到对方的值。<br>创建ThreadLocal对象时，我们可以指定泛型，这样我们就不需要每次对使用get()方法返回的值作强制类型转换了；并且我们也可以设置初始值。</p>
<p>2.如何访问ThreadLocal变量<br>一旦创建了一个ThreadLocal变量，你可以通过如下代码设置某个需要保存的值：<br><code>myThreadLocal.set(&quot;初始值”);</code><br>可以通过下面方法读取保存在ThreadLocal变量中的值：<br><code>String threadLocalValue = (String) myThreadLocal.get();</code><br>get()方法返回一个Object对象，set()对象需要传入一个Object类型的参数。</p>
<ol start="3">
<li>测试代码<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br></pre></td><td class="code"><pre><span class="line">public class Test &#123;</span><br><span class="line"></span><br><span class="line">	private static ThreadLocal&lt;String&gt; threadLocal;</span><br><span class="line"></span><br><span class="line">	public static void main(String[] args) &#123;</span><br><span class="line"></span><br><span class="line">		threadLocal = new ThreadLocal&lt;String&gt;() &#123;</span><br><span class="line"></span><br><span class="line">			@Override</span><br><span class="line">			protected String initialValue() &#123;</span><br><span class="line">				return &quot;初始化值&quot;;</span><br><span class="line">			&#125;</span><br><span class="line"></span><br><span class="line">		&#125;;</span><br><span class="line">		</span><br><span class="line">		for (int i = 0; i &lt; 10; i++)&#123;</span><br><span class="line">			new Thread(new MyRunnable(), &quot;线程&quot;+i).start();</span><br><span class="line">		&#125;</span><br><span class="line"></span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	public static class MyRunnable implements Runnable &#123;</span><br><span class="line"></span><br><span class="line">		@Override</span><br><span class="line">		public void run() &#123;</span><br><span class="line">			String name = Thread.currentThread().getName();</span><br><span class="line">			System.out.println(name + &quot;的threadLocal&quot;+ &quot;,设置为&quot; + name);</span><br><span class="line">			threadLocal.set(name);</span><br><span class="line">			try &#123;</span><br><span class="line">				Thread.sleep(1000);</span><br><span class="line">			&#125; catch (InterruptedException e) &#123;&#125;</span><br><span class="line">			System.out.println(name + &quot;:&quot; + threadLocal.get());</span><br><span class="line">		&#125;</span><br><span class="line"></span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
</ol>
<p>打印结果：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line">线程1的threadLocal,设置为线程1</span><br><span class="line">线程4的threadLocal,设置为线程4</span><br><span class="line">线程3的threadLocal,设置为线程3</span><br><span class="line">线程2的threadLocal,设置为线程2</span><br><span class="line">线程0的threadLocal,设置为线程0</span><br><span class="line">线程6的threadLocal,设置为线程6</span><br><span class="line">线程5的threadLocal,设置为线程5</span><br><span class="line">线程7的threadLocal,设置为线程7</span><br><span class="line">线程8的threadLocal,设置为线程8</span><br><span class="line">线程9的threadLocal,设置为线程9</span><br><span class="line">线程3:线程3</span><br><span class="line">线程4:线程4</span><br><span class="line">线程8:线程8</span><br><span class="line">线程6:线程6</span><br><span class="line">线程2:线程2</span><br><span class="line">线程5:线程5</span><br><span class="line">线程9:线程9</span><br><span class="line">线程1:线程1</span><br><span class="line">线程7:线程7</span><br><span class="line">线程0:线程0</span><br></pre></td></tr></table></figure></p>

      
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